Sum of all substrings of a number | GfG POTD | 24-05-2025 | GfG Problem of the day | GeeksforGeeks

🌟 GeeksforGeeks Problem of the Day | Sum of All Substrings (Optimized Logic + Dry Run) | 24-May-2025 📅
#sumofsubstrings #dynamicprogramming #gfgpotd #nileshcodes #cpp #java

🧮 In this video, we break down the Sum of All Substrings problem — a clever use of digit contribution logic combined with dynamic calculation. You’ll learn how to compute the sum of all substrings of a given number string in linear time with constant space!

🎯 Problem Summary:
Given a string s consisting of digits, compute the sum of all possible non-empty substrings treated as numbers. Leading zeros are allowed, and the final result fits in a 32-bit integer.

🧠 Examples:
Input: "6759" → Output: 8421
Input: "421" → Output: 491

📘 Concepts Covered:

Optimized digit-contribution logic
Iterative right-to-left traversal
Rolling multiplier technique (place_value)
Full dry-run with "123" to visualize how digits contribute
C++ and Java implementation explained
Time Complexity: O(n) | Space Complexity: O(1)

🔍 What you’ll learn in this video:
🔸 Why recursion or brute-force is unnecessary here
🔸 How to reduce time and space via digit-weight contributions
🔸 Visual walkthrough of how each digit forms multiple substrings
🔸 Explanation of the multiplier logic behind the formula
🔸 Debug-friendly code comments and dry-run insights

📂 GitHub Code: github.com/imnilesh18/GfG-POTD/blob/master/05_May/…
📺 Full Playlist: github.com/imnilesh18/GfG-POTD

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🔖 Tags:
#sumofallsubstrings #gfgpotd #dryrun #dsaproblems #cpp #java #nileshcodes #LeetGeek #digitcontribution #dsa #stringproblems #gfg #dynamicprogramming